This invention relates to the field of phototypesetting machines.
In so-called second generation phototypesetting machines, characters formed upon a moving character disc or drum are selectively illuminated in order to "flash" the desired characters which in turn causes images of the characters photographically formed upon the font disc, to be projected upon a photosensitive receptor sheet as is well understood by those skilled in the art. Where multiple character sizes are to be formed upon the photosensitive receptor sheet, it is highly desirable to increase the light flux for larger character sizes and to decrease the flux for smaller ones in order not to over or under expose the photosensitive receptor sheet. Generally, such compensation is effected by placing filters over the projection lenses, or in the alternative, by mechanically adjusting the diameter of an "f" stop. These methods are costly and unreliable.